There is a continuing need to improve the flame, heat, and electric arc flash protection of industrial clothing such as that worn by petro-chemical workers, pilots, firefighters, electrical workers, and steelworkers, among others. This is particularly critical for personnel who are frequently at close quarters where heat, flame and electrical arc flash hazards occur. Select military end uses also have value for such garments. The primary line of protection is the fabric in the protective clothing worn by the individual. Also important is that the clothing look good and feel comfortable, to ensure that it will be worn by the individual facing these hazards.
Flame retardant or flame resistant fibers, which can include oxidized polyacrylonitrile fibers, provide excellent heat and flame resistance. However, some challenges when working with such fibers can include brittleness, poor textile processing, and non-durable textile materials. By contrast, conventional natural and synthetic fibers (including the range from staple to continuous filament), are suitable for preparation of clothing fabrics, but lack flame resistant and/or flame retardant properties.
U.S. Pat. No. 5,763,103 to McCullough describes flame retardant and flame resistant yarns including a biregional carbonaceous fiber which is prepared from what is referred to as a biregional precursor fiber. The biregional precursor fiber includes a sheath of an oxidation stabilized thermoset polymeric material. The biregional carbonaceous fiber is prepared by the “carbonization” of the biregional precursor fiber where the fiber is exposed to an elevated temperature in an inert atmosphere to provide new carbon-to-carbon linkages resulting in what is described as McCullough's biregional carbonaceous fiber.